The traditional folding knife, sometimes also known as a pocket knife, has one or more blades pivotably mounted within a housing or casement. To prevent accidental opening of the knife, each blade typically is biased in the closed position by a mechanism such as a spring or detent. To open the blade, the user must insert the thumbnail of one hand into a notch or groove provided for that purpose near the back edge of the blade, and manually rotate the blade around its pivot point at one end of the knife body while holding the body with the other hand. This opening technique can be difficult to accomplish, particularly for those having short thumbnails or for a handicapped person who may not have full use of both hands, or with knives whose blade pivot mechanism is relatively stiff. Women, who customarily have longer fingernails than men, are hesitant to use a pocket knife because they are apt to damage or break the thumbnail used to open the blade. Moreover, it is essential in some jobs, such as commercial fisherman and paratrooper, to open and use a knife with one hand while the other hand is otherwise occupied.
Folding knives with various mechanisms for opening or assisting with opening the blade are known in the art. For example, U.S. Pat. No. 249,896 discloses a knife equipped with a handle for unloading the spring force that normally keeps the blade closed. The blade also has the conventional thumbnail notch; the user, after first manipulating the handle to remove spring force from the blade, must then open the blade using the thumbnail notch as usual. This arrangement appears relatively awkward to implement, because the user must grasp the knife in one hand while manipulating the handle with the other hand, and then use the thumb and forefinger of that other hand to pivot the blade outwardly from the handle.
The so-called switchblade knife, where the closed blade is under spring tension and opens at the touch of a button, is illegal in many jurisdictions. Furthermore, the side-opening switchblade requires a safety device, usually a sliding button, so that the knife will not open accidentally in one's pocket. This safety must be manually moved to the off position prior to opening the knife, so that one must initially position the knife in one hand to operate the safety and then reposition the knife to press the button which releases the spring-tensioned blade. This is a time-consuming and awkward movement.
U.S. Pat. No. 22,620 discloses a folding knife with a handle directly connected to the pin which pivotably mounts the blade in the handle. U.S. Pat. No. 2,416,277 shows a pocket knife having a rack-and-pinion arrangement for opening or closing the blade when a sliding bar is moved longitudinally along the blade housing. These arrangements, in common with the first-mentioned prior patent, have various practical disadvantages, among which is the need for using two hands when opening the blade.
U.S. Pat. No. 4,719,700 by the present inventor discloses a folding knife designed for opening a blade by moving an actuator button longitudinally along the blade housing. This arrangement represents a step forward in the art, as it allows the user to open the knife with only one hand. However, the operating mechanisms employed with the knife disclosed in that patent required a considerable amount of straight-line force applied to the sliding actuator, particularly when overcoming the inertia of the blade at rest. Furthermore, a knife using the rack and pinion drive disclosed in that patent would be much thicker than the conventional pocket knife and would be less appealing in appearance.